Ngene et al.
Status and trends of the elephant population in the Tsavo–Mkomazi ecosystem
Shadrack Ngene,1* Steve Njumbi,2 Martha Nzisa,1 Kenneth Kimitei,1 Joseph Mukeka,3 Shadrack Muya,4 Festus Ihwagi 5 and Patrick Omondi 6
1 Kenya Wildlife Service, Biodiversity Research and Monitoring, Tsavo Conservation Area, PO Box 14, Voi, Kenya 2 International Fund for Animal Welfare, PO Box 25399 – 00603, Nairobi, Kenya 3 Kenya Wildlife Service, Biodiversity Research and Monitoring, GIS Unit, PO Box 40241 – 00100, Nairobi, Kenya 4 Jomo Kenyatta University of Agriculture and Technology, PO Box 62000 – 00200, Nairobi, Kenya 5 Save the Elephants, PO Box 54667 – 00200, Nairobi, Kenya 6 Kenya Wildlife Service, Biodiversity Research and Monitoring, Species Conservation and Management, PO Box 40241 – 00100, Nairobi, Kenya *Corresponding author email: [email protected] or [email protected]
Abstract This paper updates the data on the population status of elephants in the Tsavo–Mkomazi ecosystem. Data were acquired through aerial census of elephants in the ecosystem, from 7 to 12 February 2011. The census covered an area approximately 48,319 km2, which was divided into 44 counting blocks. Each block was assigned to a specific aircraft; the crew consisted of a pilot, front-seat observer and two rear-seat observers for the four-seater light aircraft, and a pilot and an observer for a two-seater light aircraft. The census lasted five days and involved nine light aircraft and about 252 hours of actual counting time, representing a mean search rate of about 191 km2/hr. A total of 12,573 elephants were counted, indicating a modest increase of 2% after the 2008 census and a 96% increase after the 1988 census (n = 6,399). Most elephants (69%, n = 8,614 individuals) were counted inside the protected areas; about 31% (n = 3,859 individuals) were outside protected areas. About 50% of the elephants (n = 6,214) were in Tsavo East National Park, 22% (n = 2,751) in the Taita ranches and 17% (n = 2,142) in Tsavo West National Park. A programme of providing water to elephants in the northern parts of Tsavo is recommended as well as electric fencing and establishment of administration and security structures at South Kitui National Reserve. This will create more space for the increasing population of elephants as well as improve their security.
Additional key words: aerial census, carcass, drought
Résumé Ce document met à jour les donnés sur la situation des populations d’éléphants dans l’écosystème de Tsavo- Mkomazi. Les données ont été acquises grâce à un recensement aérien des éléphants dans l’écosystème, du 7 au 12 février 2011. Ce recensement a couvert une superficie d’environ 48.319 km2, qui était divisée en 44 blocs de comptage. On avait assigné à chaque bloc un avion spécifique, l’équipage étant composé, pour l’avion léger à quatre places, d’un pilote, d’un observateur sur le siège avant et de deux observateurs sur le siège arrière, et pour un avion léger biplace, d’un pilote et d’un observateur. Le recensement, auquel ont participé neuf avions légers, a pris cinq jours et environ 252 heures de temps de comptage réel, ce qui représente un taux de recherche moyen d’environ 191 km2/heure. Un total de 12.573 éléphants ont été dénombrés, ce qui indique une légère augmentation de 2% après le recensement de 2008 et une augmentation de 96% après le recensement de1988 (n = 6.399). La majorité des éléphants (69%, n = 8.614 éléphants) ont été comptés à l’intérieur des aires protégées; environ 31% (n = 3.859 éléphants) étaient en dehors des aires protégées. Environ 50% des éléphants (n = 6,214) étaient dans le Parc national de Tsavo-Est, 22% (n = 2,751) dans les ranchs de Taita et 17% (n = 2,142) dans
38 Pachyderm No. 53 January–June 2013 Status and trends of the elephant population in the Tsavo–Mkomazi ecosystem le Parc national de Tsavo Ouest. Un programme d’approvisionnement en eau pour les éléphants au nord de Tsavo est recommandé ainsi que les clôtures électriques et une mise en place des structures administratives et sécuritaires dans la Réserve nationale du sud-Kitui. Cela va créer plus d’espace pour l’augmentation de la population d’éléphants ainsi qu’améliorer leur sécurité.
Mots clés supplémentaires : recensement aérien, carcasse, sécheresse
Introduction parks. The proportion of ‘recent’ carcasses however did not change significantly, confirming illegal killing The Tsavo ecosystem is home to Kenya’s largest was still taking place through 1988 when the ‘recent’ elephant population (Blanc et al. 2007). This popula- carcass ratio peaked at 6.69%. Despite this, the 1989 tion was over 35,000 animals by the end of 1974 (Cobb count was the first authoritative confirmation that the 1976) and about 11,733 in 2008 (Omondi et al. 2008). elephant population was on a recovery course, a trend The February 2011 dry season census was conducted one observed till 2008. year after the severe drought of 2009 to early 2010 when The 2002 wet season survey was undertaken as part it was feared that many elephants (Loxodonta africana) of Kenya Wildlife Service (KWS) and Monitoring of had succumbed, as had happened during the unusually Illegal Killing of Elephants (MIKE) joint initiatives dry conditions of 1970 and 1971 that led to elephant to establish the status of Tsavo’s elephant population mortality of unanticipated magnitude. Between 6,000 and provide baseline data on poaching. The count and 9,000 elephants died in the eastern sector of Tsavo revealed that the Tsavo population had increased by National Park (Corfield 1973; Cobb 1976). 5% since 1999, from 8,068 to 9,284 (Kahumbu et al. The ecosystem has been the subject of detailed 1999). Fifty percent (n = 10) of the recent carcasses sample and total aerial counts since the early 1960s. were recorded in Galana, where poaching pressure Recent total counts include Olindo et al. (1988), was high in the 1970s and 1980s. The figure could Douglas-Hamilton et al. (1994), Kahumbu et al. have been an underestimate as the thick vegetation (1999), Omondi et al. (2002), Omondi and Bitok may have obscured some carcasses. The census noted (2005) and Omondi et al. (2008). Past sample counts a remarkable increase in livestock in the protected include those by Cobb (1976), Leuthold (1976), areas from about 820 animals in 1999 to about 5,190 WCMD (1976), IUCN (1978) and Inamdar (1996). animals in 2002 (Omondi et al. 2002). Both sample and total counts in the 1970s showed It is important to caution against direct comparisons remarkably high numbers of elephants, though sample of results of past aerial counts due to different counts appear to have overestimated the numbers by methodologies, counting effort and climatic conditions a wide margin—almost twice the total count figures. between the years (Douglas-Hamilton et al. 1994). For The 1988 counts showed a 75% decline in elephant instance, this possibly explains the large discrepancies numbers within the protected areas and a further 87% observed between sample and total counts in the decline in the adjacent non-protected areas since the 1970s. Over the years, elephant densities varied 1972 total counts (Olindo et al. 1988). Two major considerably both by blocks and through time, from factors have contributed to the observed overall as low as 0.002 elephants/km2 in Galana to as high as continental decline of elephant numbers: reduced 0.921 elephants/km2 in Tsavo East south (Douglas- carrying capacity of Africa for elephants due to habitat Hamilton et al. 1994; Kahumbu et al. 1999; Omondi et change, and hunting for ivory (Milner-Gulland and al. 2002; Omondi and Bitok 2005; Omondi et al. 2008). Beddington 1993a,b). Since 1988, there has been Surface water availability and security are believed to a steady increase in elephant numbers. The 1988 be the major factors influencing elephant distribution. distribution of ‘recent’ carcasses confirmed heavy In 2002, a dramatic shift in elephant distribution was poaching was still rampant, especially on the periphery observed between Tsavo East north and Tsavo East of the parks, and the older carcasses confirmed that south, as the former had received more rainfall prior poaching had taken place in the heart of the reserves to the count (Omondi et al. 2002). Understanding these in the early 1980s. The distribution of elephants in ecosystem-use dynamics by elephants and other large 1989 confirmed that elephants previously counted mammals is important in their management. along the periphery had moved further inside the
Pachyderm No. 53 January–June 2013 39 Ngene et al.
The goal of the 2011 aerial survey was to sustain the long-term aerial monitoring of elephants in the Tsavo–Mkomazi ecosystem. This consistent monitoring programme Kenya SK began in early 1999 and has been closely and accurately monitoring Ta nzania the status and trends of elephants 26 and other large mammals since 23 22 then. Therefore, it is important to continue with the tri-annual 2 G1 19 G2 1 G4 aerial census of elephants in the 27 G3 CW Tsavo–Mkomazi ecosystem. The 3 18 20 information generated will show 5 4 G5 G6 the number, density and distribution 21 RB of elephants in the ecosystem. 7A 17 16 The information will be used by 6 park managers and policymakers 24 13 to make management decisions 15 regarding the management of 8 11 14 25 emerging trends and distribution 9A of elephants in the ecosystem. 10A 12A 9B 10B MN Materials and methods 12C N MC Study site Tanzania The Tsavo–Mkomazi ecosystem MS consists of an area of about 48,319 Indian 2 Ocean km (Cobb 1976). The ecosystem 0 12.5 25 50 75 100 km lies between 2–4°S, and 37.5– 39.5ºE. Common rivers traversing the ecosystem include Galana, Voi, major river Chyulu National Park (NP) Tsavo West NP counting block Tsavo East NP north South Kitui Tiva, Tsavo and Athi (Figure 1). National Reserve The ecosystem’s mean annual Taita ranch Tsavo East NP south rainfall varies locally between 250 national boundary Mkomazi NP (north, central and south) and 500 mm (Leuthold 1978). Most Figure 1. Counting blocks used during the aerial count of elephants and of the rain falls in two rainy seasons: other large mammals in the Tsavo–Mkomazi ecosystem (7–12 February in March–May and November– 2011). Blocks 7B, 9A, 10A, 12B and RB cover the Taita ranches, blocks December (Tyrrell and Coe 1974); G1–G6 represent Galana ranches, blocks 24 and 25 represent other June through October constitutes a ranches east of the ecosystem, and blocks 13, 14 and 15 represent the long dry season (Leuthold 1978). Ndii–Ndara plains. (Source: KWS, 2011.) The terrain of the Tsavo– Mkomazi ecosystem is generally structure and chemical and physical properties. The flat and undulating in the southeastern and northern soils are rich in quartz and ferruginous gravel, with sections (Leuthold 1978). Mukeka (2010) provides finer sand cemented by a red lateritic crust. Sand and a detailed description of the ecosystem’s terrain. gravel of the alluvial soils are cross-bedded together Generally, the area lies about 300–500 m above sea along the river loops of the Galana (Leuthold 1978). level. The soils of the Tsavo–Mkomazi ecosystem The vegetation consists of remnants of formerly show a wide range in depth, colour, drainage condition, extensive Commiphora–Acacia woodlands that
40 Pachyderm No. 53 January–June 2013 Status and trends of the elephant population in the Tsavo–Mkomazi ecosystem have been destroyed or at least thinned out by elephants (Cobb 1976). The vegetation communities in the ecosystem are described in detail by Napier-Bax and Sheldrick (1963), Laws (1969, 1970), Tyrrell and Coe (1974) and Mukeka (2010). The major herbivores are elephant (Loxodonta africana), African buffalo (Syncerus caffer), eland (Taurotragus oryx pattersonianus), fringe-eared oryx (Oryx beisa callotis), Coke’s hartebeest (Alcelaphus buselaphus cokii), Burchell’s zebra (Equus burchelli), impala (Aepyceros melampus), giraffe (Giraffe camelopardalis) and Grant’s gazelle (Gazella granti) (Cobb 1976).
Census blocks design The aerial count followed the method described by Douglas-Hamilton (1996). The aircraft N consisted of two-seater crew Supercabs or four seater crew Cessnas. Forty-four counting blocks, as designed for previous censuses, were adopted for ease of comparing findings. Flight lines of 1-km spacing were designed to ensure that all elephant herds and large major river ight lines mammals were sighted and counted (Figure 2). block boundary 0620 40 080 100 km The blocks are defined mostly by recognizable features like roads, rivers, hills and protected area boundaries, except for the Voi triangle Figure 2. Flight lines used during the aerial count (7–12 and blocks 13–17. The blocks were of suitable February 2011) in the Tsavo–Mkomazi ecosystem. sizes that could be flown in a day by one or two teams. The average block size was 1,098 flight paths. The GPS units were set to Universal km² (SE = ±445 km²; n = 44). The smallest block Transverse Mercator kilometre grids on both north (block 21) measured 248 km² and the largest (block and south axes. The teams took off at dawn, ensuring 12C) 2,008 km². In the larger blocks, two planes were that counting started before the day got hot. Parallel deployed to count simultaneously to ensure counting lines were flown, whose interval was determined by was completed within a day. the front observer and the pilot based on terrain and visibility. Fuel was strategically distributed in the Aircraft and crew various airstrips in the ecosystem for convenience of refuelling from blocks distant from the counting Nine fixed-wing aircraft (Cessna and Husky) with centre. In a few blocks, the topography influenced the high wings to give an unobstructed ground view were flight paths as rugged terrain was avoided. used during the six-day event. The crew comprised a pilot and one front-seat observer for a two-seater aircraft, and a pilot, one front-seat observer and two Data recording and cleaning rear-seat observers for a four-seater aircraft. Each The aerial census took place from 7 to 12 February team was given the flight maps of assigned blocks 2011. Most of the crew members were highly the evening before to allow the team to plan for the experienced. Test flights were conducted a day before next day. A geographical positioning system (GPS) the actual counting commenced to familiarize and was used for navigation and to record waypoints and refresh the crew. Speeds of approximately 130–180
Pachyderm No. 53 January–June 2013 41 Ngene et al. km/hr and heights of about 200–400 ft (60–120 m) 1997; Mitchell 2009). General distribution patterns above ground level were maintained. Blocks separated (random, dispersed or clustered) and distribution of by rivers were counted simultaneously to minimize herd sizes were analysed for elephants. We tested double count or omission due to elephants crossing the for the general distribution patterns of the elephants river. Pilots flew overlaps of approximately 1–2 km using the Getis-Ord general G statistic as described into the adjacent blocks to ensure that herds moving by Mitchell (2009). The distribution of different herd into the block were not missed by either team. Both sizes was mapped using the hot/cold-spot analysis; dead and live elephants were counted. Where large Getis-Ord Gitrations of large (hot spots) and small herds were encountered, the pilots circled to give (cold sports) groups of elephants were sighed during observers ample time to count. Elephant carcasses the aerial survey (Esri 2007; Mitchell 2009). Z scores were classified as ‘fresh’, ‘recent’, ‘old’ or ‘very were used for interpretation of significance levels old’, as described by Douglas-Hamilton and Hillman of statistical tests (Zar 1996). High positive Z score (1981). For analyses, the first and second categories indicates a higher clustering for locations with large were pooled as ‘recent’, and the third and fourth as numbers of elephants while negative Z score indicates ‘old’. Standard codes were used to denote elephants clustering of areas with small groups of elephants. and the different categories of carcasses. Front-seat The results were interpreted as described in detail by observers cleaned the data sheets when necessary Mitchell (2009). before handing them over to the data entry team. To analyse the relationship between elephant Waypoints and tracks were downloaded onto ArcGIS distribution and water pans (dry and wet) and rivers, a 9.3. The tabulated species data were added onto kernel density of the elephant was created as described the ArcGIS software and a spatial join was created by Mitchell (2009) using a search radius of 24 km based on the waypoint (Mitchell 2009). The file was (Mukeka 2010). A simple density surface for water converted into a shape file for each block. Duplicates in pans (dry and wet) and distance surface for rivers was the zones of overlap of adjacent blocks were identified created as described by Mitchell (2009). Using spatial and corrected before merging all datasets into one for analyst tool in ArcGIS 9.3, the raster cell values of the analysis and preparation of distribution maps. respective surfaces were extracted onto the elephant count point shape-file (Esri 2007). Then the extracted values were exported into an MS Excel spreadsheet to Data analysis obtain a set of elephant density data against distance For regression analysis, data were pooled for areas to water pans and rivers. A simple correlation analysis that were consistently surveyed from 1988 to 2011. was performed using this data as described by Zar These areas included Tsavo East (north), Tsavo East (1996). The strength of the correlations was interpreted (south), Tsavo West, Mkomazi NP, and Galana and following guidelines described by Fowler et al. (1998). Taita ranches. The regression analysis followed the The proportion of recent to old was calculated as procedures described by Zar (1996). Fourth-order an index of the previous year’s mortality (Douglas- polynomial analysis was used to get the line of best Hamilton 1996), noting that 2009 to early 2010 was fit during the regression analysis (Zar 1996). marked by a severe drought. The observed rate of population increase (¯r ) was calculated from the natural logarithms of the total Results number of elephants counted in 1988 and 2011 using the formula (Caughley 1977): Aerial census effort A total of about 252 hours of actual counting time ¯r = logeNt – logeN0 was spent during the census. This represents a mean search rate of about 191 km2/hr or 5.2 hours for every where loge = natural logarithm; Nt = total number 1,000 km2 in a counting area of about 48,319 km2. The of elephants counted in 2011; N0 = total number of elephants counted in 1988. search rate was more intense than the aerial counts in The orientation of elephant distribution and the 1988, 1994 and other preceding counts (see Olindo centre of their concentration were analysed using the et al. 1988; Douglas-Hamilton et al. 1994; Omondi standard deviational ellipse and mean centre (Esri et al. 2002; Omondi and Bitok 2005; Omondi et al.
42 Pachyderm No. 53 January–June 2013 Status and trends of the elephant population in the Tsavo–Mkomazi ecosystem – – – – – – 2008) although the difference in the number – of hours spent per 1,000 km2 during this 3,540 6,825 3,540 1,394 1,358 4,073 1962 census and those of past aerial census (1988 10,365 – – – – – – – to 2008) was not statistically significant. – 2,238 4,744 8,056 1965* 15,038 Status and trends of elephants 15,038 – – – – – –
The estimate for the February 2011 aerial 500 3,464 2,964 8,134 5,709 6,619 1969* 23,926 census was 12,573 elephants in the Tsavo– 20,462 – – – – – – – Mkomazi ecosystem, representing a modest 0 100 increase of about 2% in the last three years 100 6,592 6,008 1970* 12,700 (Table 1). Of these elephants 69% (n = 12,600 – – – 8,614) were counted inside the parks and – 300 5,914 1,235 4,379 2,067 4,328 6,633 6,435
31% (n = 3,859) outside the parks. About 1972 25,377 19,463 50% (n = 6,214) of the elephants were in – – – – – Tsavo East NP, 22% (n = 2,751) in the Taita – 500 500 9,208 3,955 9,011 1973 22,674 ranches and 17% (n = 2,142) in Tsavo West 22,174 NP (Table 1). The number of elephants – – – – – 79 667 increased from about 6,399 in 1988 to 220 6,449 1,155 5,294 1,076 1,938 2,469 about 12,573 in 2011, which represents a 1978* – – – 96% increase in 23 years. From 1999 (n = – 90 93 853 9,447), the population increased by 33%. A 770 6,399 1,979 4,420 1,036 1,274 2,283 fourth-order polynomial regression analysis 1988 – on trend of elephant numbers from 1988 – 46 74 11 966 193 642 134 6,999 1,728 5,271 2,106 to 2011 showed an increase in elephant 3,020 1989 population during the period (R2 = 0.99, n = – – – 50 9, Figure 3). The estimated observed rate of 50 131 450 8,407 3,157 5,250 1,644 1,413 1,233 3,436 population growth over the 23-year period 1991 was 0.68, representing an approximate – – 26 46 446 287 302 annual growth rate of 0.03. 399 8,032 1,466 6,566 1,107 3,132 2,733 1994 Distribution and density of – – 30 12 27 77 3221 elephants 1337 9,447 2,693 6,754 1,391 1,245 2,119 1999 Figure 4 shows the distribution of elephants – 2 0 35 14 in the ecosystem. Most of the herds were 63 940 828 9,284 8,344 2,168 2,087 4,089 found in Tsavo East NP, within about 45 2002 km north and south of the Galana River. – 1 0 31 11 High densities of about 1 elephant/km2 41 2,680 9,062 1,376 1,292 2,626 3,896 2,499 2005 were recorded in Tsavo East NP, south of 11,742 0 8 the Galana River (Figure 5). 0 38 130 308 The elephants exhibited a highly 131 1,584 1,108 2,161 3,731 4,118 2008 11,733 clustered distribution (Z score = 5.36, 10,149 0 P = 0.01, critical value = 2.58). Taita 0 168 509 398 256 135 3,959 8,614 2,751 2,142 4,120 2,094
ranches have the largest herds of elephant 2011 12,573 concentration while the smallest herds are found in Tsavo East north of the Galana River. The mean centre of the distribution was within the Ndara plains in Tsavo East NP, south of the Galana River (Figure 6). Source: Leuthold 1973; Olindo et al. 1988; Douglas–Hamilton 1994; Kahumbu 1999; Omondi 2008 Source: collected in late 1999 to 2011, data were using the total count method. From acquired using the sample counts method; in years without *, data were acquired * Data in that year were collected in June, immediately after the April–May wet season. to 1994 data were January or early February (dry season); from1962 N = north, S south, NP national park, NR reserve. – Periods when no aerial census took place in the location. Total Total (non-parks) Total Total (parks) Total Outside Other blocks Rombo Taita Taita Galana Mkomazi NP South Kitui NR Chyulu NP Tsavo West Tsavo Tsavo East (S) Tsavo Tsavo East (N) Tsavo Table 1. Elephants counted in the Tsavo–Mkomazi ecosystem from 1962 to 2011 (no.) ecosystem from 1. Elephants counted in the Tsavo–Mkomazi Table Area
Elephants occurred as individuals (n = 213
Pachyderm No. 53 January–June 2013 43 Ngene et al.
14 herds) or in groups (n = 1,195 herds). The herd sizes ranged from 2 to 189 animals with ±95% confidence 12 interval of herd sizes being 10–11 elephants. The
10 observed and expected size of elephant herds was significantly different Χ( 2 = 1,725, df = 9, P < 8 0.05). Larger herds of elephants were found in the
6 Taita ranches, southern parts of Tsavo West NP (Njukini and Jipe areas) and north Mkomazi NP 4 3 2 Number of elephants (’000s) 4 y = –0.141x + 1,135.x – 3E + 06x + 5E + 09x – 2E + 12 R2 = 0.999 (Figure 7). The smallest herds of elephants were counted north to northeast and south of the Galana 2 River in Tsavo East NP (Figure 7). High densities 0 of elephants occurred close to wet water pans and 1985 1990 1995 2000 2005 2010 2015 Year rivers; low densities were recorded near dry water pans (wet water pans: r = 0.90, n = 1,408, P < 0.05; dry water pans: r = 0.19, n = 1,408, P < 0.05). There Figure 3. Total aerial count estimates of the Tsavo– was a weak negative relationship between elephant Mkomazi ecosystem elephant population, 1988–2011. density and distance to water pans (r = 0.37; n = 1408; P < 0.05).
SK Number, density and distribution of elephant carcasses 26 A total of 567 elephant carcasses were 23 22 recorded during this census. Table 2 provides a summary of the number 2 G1 19 G2 of carcasses counted during the aerial 1 G4 27 G3 CW census, including the carcass ratio. In 3 2008 there were only 8 recent carcasses; 18 20 5 4 G5 G6 in 2011, 48 recent carcasses were 21 seen, which represents an increase of RB 7A 17 16 about 600%. The carcass ratio also 6 increased from 0.6% in 2008 to 4.3% 24 7B 13 15 in 2011. High carcass density (about 0.031–0.037 km2) was recorded in 8 11 14 25 Tsavo East NP south of the Galana River 9A 10A (Figure 8), and modest (about 0.02 km2) 12A 2 9B 10B and lowest (0.001–0.008 km ) carcass MN 12C densities were recorded in Tsavo East NP north of the Galana River and Tsavo Tanzania MC West NP; and, the rest of the remaining Indian areas (Figure 8). Figure 9 provides a MS Ocean summary of the general distribution of the elephant carcasses according to age Elephant distribution class in the Tsavo–Mkomazi ecosystem. 1–7 major river N 8–19 protected area 20–45 Taita ranches Figure 4. Distribution of elephant herds 46–90 counting block in the Tsavo–Mkomazi ecosystem. No 91–189 0510 20 30 40 km national boundary elephants were counted in South Kitui National Reserve (SK).
44 Pachyderm No. 53 January–June 2013 Status and trends of the elephant population in the Tsavo–Mkomazi ecosystem
South Kitui NP
Tsavo East NP 26 Chyulu NP 23 Tiva River 22
2 G1 Athi River 19 G2 1 G4 27 G3 CW 3 18 20 5 4 G5 G6 Tsavo River Galana River 21 RB 7A 17 16 6 Tsavo 24 West NP 7B 13 15
8 11 14 25 9A 10A N 12A 9B 10B N MN 12C
MC Indian MS Indian Tanzania Ocean Tanzania Ocean
0510 20 30 40km
value Elephant densities (no./km2) high: 1.58 major river 0.062–0.244 0420 06080 100 km protected area 0.307–0.427 low: 0 Taita ranches 0.609 0.791 standard deviation ellipse 0.974 mean centre counting block national boundary Figure 5. Elephant densities in the Tsavo–Mkomazi ecosystem (7–12 February 2011). Figure 6. Kernel density of elephants in the Tsavo– Mkomazi ecosystem; mean centre and standard deviational ellipses based on data collected 7–12 February 2011. (J Mukeka, KWS GIS section)
Table 2. Elephants and elephant carcasses counted in theTsavo–Mkomazi ecosystem (no.), 1988–2011 Carcass ratio Elephants Recent Total dead (dead/dead plus Std natural Carcass ratio Year (no.) dead (no.) (no.) live) (%) mortality @ 4% recent (%) 1988 5,363 162 2,421 31.1 215 2.9 1989 6,033 115 1,752 22.5 241 1.9 1991 6,763 4 1,210 15.2 271 0.1 1994 7,371 1 1,362 15.6 295 0.0 1999 8,068 6 427 5.0 323 0.1 2002 9,284 14 302 3.2 371 0.2 2005 10,397 6 138 1.3 416 0.1 2008 11,696 4 68 0.6 468 0.0 2011 12,573 48 567 4.3 497 0.4 Old carcasses are calculated by subtracting recent dead from total dead. The old carcasses include ‘very old’ and ‘old’ carcasses; recent dead include ‘fresh’ and ‘recent’ carcasses.
Pachyderm No. 53 January–June 2013 45 Ngene et al.
SK
26 23 r 22 Tiva Rive
2 G1 19 G2 G3 Athi River 1 G4 27 CW 3 18 20 5 Ts 4 G5 G6 avo River Galana River 21 RB 7A 17 16 6 24 7B 13 15
8 11 14 25 9A 10A 12A 9B 10B MN N 12C
MC
MS Carcass densities (no./km2) 01020406080 km < –2.0 N –2.0 to –1.0 Elephant hot/cold spots –1.0 to 1.0 GiZ core 1.0 to 2.0 020406080 100 km < –2.0 Chyulu West Taita ranches > 2.0 –2.0 to –1.0 Galana ranch Tsavo East NP north –1.0 to 1.0 Mkomazi NP Tsavo East NP south 1.0 to 2.0 other areas Tsavo West NP 2 > 2.0 Figure 8. Elephant carcass densities (no./km ) in the Tsavo–Mkomazi ecosystem (early February 2011). Figure 7. A hot spot analysis of the locations with different sizes of elephant herds in the Tsavo–Mkomazi ecosystem. Large herds of elephants (Z score = > 1.0) 131). Specifically, the 2009 and early 2010 droughts were recorded in the Taita ranches, northern parts of were responsible for these natural deaths, with more Mkomazi NP and southern and western parts of Tsavo deaths in 2009 (83%, n = 366) and 2010 (52%, n = 96) West NP. High positive values of Z scores indicate than in previous years (Figure 10). Of the 674 elephant locations where large groups of elephants occurred carcasses reported in the study area between 2008 and (hot spots) whereas low negative values of Z scores 2010, 86% (n = 576) had the two tusks recovered, 1% indicate where smaller groups of elephants (cold spots) were sighted during the aerial survey. (n = 9) had one tusk recovered and 13% (n = 89) had no tusks recovered (KWS-TCA 2011). Also, most of the carcasses were classified as ‘old’ (91%, n = Discussion 517), a category for elephants that had been dead for The results revealed that the population of elephants more than one year (Douglas-Hamilton 1996). This in the Tsavo–Mkomazi ecosystem increased from period coincides with the period when the study site 11,733 in 2008 to 12,573 in 2011, representing a 2% experienced a drought. The drought led to scarcity of increase in three years. Compared with the rate of forage and water culminating in the starvation of many increase between 2005 and 2008 (4%), this represents elephants. Most of the old carcasses were recorded a 2% decrease in population change between 2008 in Tsavo East and northern parts of Tsavo West NPs; and 2011. The decreasing rate of increase could be these were the areas that lacked water during the attributed mainly to natural mortality (Figure 10). The 2009 drought. Elephants are water-dependent animals data indicate that natural causes of elephant deaths (Ngene et al. 2009), therefore many could have died were high between 2008 and 2010 (84%, n = 674) during the period due to lack of water. compared with deaths from 2005 to 2007 (16%; n = Search effort during aerial counts determine the
46 Pachyderm No. 53 January–June 2013 Status and trends of the elephant population in the Tsavo–Mkomazi ecosystem
number of large mammals counted during the
SK exercise (Douglas-Hamilton et al. 1994). This report uses the term ‘search effort’ to refer to the area (km2) covered by the aerial count crew in one hour (km2/hour) (Douglas-Hamilton et 26 23 al. 1994). High and low search efforts result in 22 higher and lower numbers of the large mammals 2 G1 G2 G3 being counted (Douglas-Hamilton et al. 1994). 1 19 G4 27 CW The 2011 aerial census recorded a search effort 3 of 191 km2/hour, which was higher than for 18 20 5 2 4 G5 G6 previous aerial census—321 km /hour in 1988, 21 2 2 RB 276 km /hour in 1989, 247 km /hour in1991, 210 7A 17 16 2 2 6 km /hour in 1994, 242 km /hour in 2002, 224 24 2 2 7B 13 km /hour in 2005, and 213 km /hour in 2008 15 (Douglas-Hamilton et al. 1994; Omondi et al. 8 11 14 25 2008). It is therefore possible that the high number 9A 10A of elephants counted in 2011 is not because of 12A 9B 10B actual population increase but due to increased MN N 12C search effort (Figure 11).
MC High density of elephants was recorded in the southern part of Tsavo East NP. The area was also MS 0510 20 30 40 50 km the mean centre where many groups of elephants
Carcass stage were counted. This area has two permanent rivers fresh (Galana and Voi) and many water pans, which Chyulu West NP Taita ranches river recent Galana ranch Tsavo East NP north are lacking in other parts of the ecosystem. old Mkomazi NP Tsavo East NP south very old High densities of elephants were recorded about other areas Tsavo West 1–15 km from the rivers and water points. Since Figure 9. Spatial distribution of elephant carcasses elephants are water-dependent animals (Estes according to different age classes in early February 2011. 1991), their density is expected to be high in Most of the carcasses were ‘old’ and ‘very old’. areas within 10–15 km from water points 400
350
300
250
200
150
100
50 Number of dead elephants
0 2005 2006 2007 2008 2009 2010
Natural Illegal *PAC Unknown
Figure 10. Number of dead elephants against causes of elephant mortality in the Tsavo Conservation Area, 2008–2010. Other causes of death include train accidents, sickness and lion predation. *PAC = problem animal control.
Pachyderm No. 53 January–June 2013 47 Ngene et al.
(Ngene et al. 2009). Analogous findings were made recent carcasses only is very low (0.4%). This further for elephants in Marsabit NP and Reserve (Ngene compels us to believe that most of the carcasses are et al. 2009), Samburu National Reserve in Kenya attributed to the drought in 2009 and early 2010. Under (Thouless 1995), Masai Mara Game Reserve in Kenya conditions of low rainfall, as experienced in preceding (Khaemba and Stein 2000), Maputo Elephant Reserve years, the rate of carcass disintegration is minimal in Mozambique (Boer et al. 2000), Serengeti NP in (Douglas-Hamilton and Hillman 1981). As a result, Tanzania (McNaughton 1990), the Kunene region more carcasses would be sighted during an aerial in northwest Namibia (Leggett 2006), the northern census. Similar to the 1970–1971 dry season census Namib Desert (Viljoen 1989), and northern Kenya (Corfield 1973), most of the carcasses were recorded (Leeuw et al. 2001). in Tsavo East along the Galana River, where elephant Despite an increase in the number of carcasses densities are apparently highest in the ecosystem. since the 2008 census (Figure 12), the population is Visibility during the 2011 survey was good as it was at on the increase. The carcass ratio calculated using the height of the dry season when vegetation is limited. Large herds of elephants were recorded 14,000 outside protected areas (Taita and Galana ranches). Possibly lack of security in these areas, 12,000 leading to incidence of elephant poaching, is forcing the elephants to congregate in large 10,000 numbers outside protected areas whereas inside our secure protected areas, the groups are small. 8,000 Similar results have been reported in Meru NP (Njumbi 1995), Queen Elizabeth NP (Abe 1994) 6,000 and Mikumi NP (Moss and Poole 1983). Number of elephants
4,000 y = –0.000x4 + 0.171x3 – 46.15x2 + 5,442.x – 23,157 R2 = 0.988 Conclusions and 2,000 recommendations
0 Conclusions 120 140 160 180 200 220 240 260 280 From the results and discussion, we conclude: Counting time (hours) • Elephant numbers in the Tsavo–Mkomazi Figure 11. Number of elephants counted in the Tsavo– ecosytem have continued to increase since Mkomazi ecosystem against the total counting hours. (Data 1988, though with a declining rate of 2% over are for 1988, 1989, 1991, 1994, 2002, 2005, 2008 and 2011.) that of the last three years (2008 to 2011). This declining rate is attributed mainly to the 35 drought of 2009 that saw a proportionately high rate of natural mortality. 30 –0.139x y = 2E + 119e • The highest elephant densities, of R2 = 0.76256 25 approximately 1 elephant/km2, were observed 20 in Tsavo East south of the Galana River.
cass ratio (%) • Elephant distribution in Tsavo–Mkomazi 15 remains clustered inside the protected areas 10 of Tsavo East NP along the Galana River and 5 its tributaries as well as in artificial water
Elephant car 0 points south of the river. 1986 1990 1994 1998 2002 2006 2010 2014 • In contrast, congregations of large herds were Year recorded outside the protected areas: in the Taita ranches between Tsavo East and West Figure 12. Trends of elephant carcass ratio in the Tsavo– NPs. However, isolated large herds were also Mkomazi ecosystem, 1985–2011. observed on the outskirts of Galana ranch,
48 Pachyderm No. 53 January–June 2013 Status and trends of the elephant population in the Tsavo–Mkomazi ecosystem
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